The purpose of this project is to examine the structural and functional evolution of neurotransmitter receptor proteins. Using muscarinic cholinergic and beta adrenergic receptors as the initial model sysems we have isolated and characterized these receptors from the brains and hearts of a wide variety of species. Brain and heart tissue have been obtained from all vertebrate classes including mammals, birds, reptiles, amphibians, and fish as well as from lower species including insects (Drosophila). Data from muscarinic receptor studies demonstrate that out of all of the parameters studied (SDS gel molecular weight, isoelectric point, monoclonal antibody cross reactivity, agonist affinity, antagonist affinity, stereospecificity of ligand binding, GTP shifts of agonist affinity, and receptor density) only receptor density appears to have changed over 900 million years of evolution gradually increasing in higher species. Muscarinic receptors have been purified from human brain, rat brain and heart, pig heart and shark brain and heart in order to compare primary structures in detail. The evolutionary relationship between muscarinic cholinergic receptors and other neurotransmitter receptors is also being studied. Protein sequence data and defined gene probes are being employed to follow the evolution of adrenergic, cholinergic and GABAergic receptors. We have cloned and sequenced beta and muscarinic genes from human and rat and have isolated a number of clones from other species. In particular, a positive clone from Drosophila genomic library has been isolated. Partial sequence data reveals that this clone contains a stretch of fifty- four nucleotides which has 84 homology with the corresponding human beta2 sequence. When the sequence is translated into amino acids and favored substitutions are considered, the homology goes up to 100. Although the exact nature of this beta2-like gene is still unknown, it may provide valuable information toward our understanding of the evolution of neural receptors. *(Transferred from LNP on 7/87).